Molecular wavefunctions of the electronic states are obtainable by the configuration interaction (CI) method. Such wave functions of a molecule in question are often difficult to interpret in terms of physical descriptions of the electronic state characteristics (electron distribution, energy localization, photoreactivity, etc). However, the configuration analysis (CA) method enables us to analyze the molecular state wavefunctions of a molecule in question ("sample molecule") quantitatively in terms of the "reference" wave functions of molecular fragments of the sample molecules. For example, CA correctly predicts the localization of the triplet excitation in the photoreactive C equals C bond of pyrone in the skin-carcinogen, Psoralens, in agreement with experiments. In effect, CA of molecular state wavefunctions can tell us where the excitation energy is accumulated (localized) or delocalized in the sample molecule. In this proposal, we plan to provide answers to the following questions: a) Structure-activity relations in carcinogens; b) What part of firefly luciferin molecules (including bioluminescent chromophores) is energized by electronic exciations, and What is the relation between CA data and bioluminescence mechanism? c) Where do singlet and triplet excitations produce the photoreactive region(s) in chlorophylls, and what is the spectral relation between Chl and Bact chl? d) Does photoexcitation of 11-cis retinal Schiff's base (protonated) preferentially excite 11-C equals C bond for isomerization leading to the vision stimulus?